Back-to-back receiver



June l, "J" M. G. cRosBY BACK-TO-BACK RECEIVER 3 Sheets-Sheet l Filed Dec. 6, 1938 BY y@ g A TTORNEY.

June 1l, 1940.

` smo-mss FREQUENCY M. G. cRosBY 2,204,342

BACK-To-BACK RECEIVER Filed Dec. 6,. 1938 3 Sheets-Sheet 2 I zoe y ...25 ...LZ/6 202) ATTORNEY.`

M. G. CROSBY BAcK-To-BACK RECEIVER Filed Dec. 6, 1938- 5 Sheets-Sheet 3 June 1l, 1940.

Patented `June v11, 1940 *Y t ,l y i UNITED y STATS. PATE-NTL*orifice Radio Corporation of America, afcorporation v vofDelawa're..v

Appliostion neoembor 6; 193s, sorisiivoeias* @12 claims iciQzso-fzoj' e l' This application concerns new and improved assume asanexample a 450`kilocycle intermedifrequency and phase modulation receivers rof vthe .ateffrequency which is -to Lbe lheterodyned to `100 back-to-back type. In my novel receiver there kilocycles. .In the system of thisinvention two are two branches which feed phase or frequency frequency. converting; detectors are arranged `s modulated wave energy to detectors with theirv o with one of the beating' oscillators tuned to 350 5 outputs connected in push-pull. The normalv kilocycles and thefotherto 550`kilocycles. y The procedure in this type of. receiver is toprovide `heatproducedby the first oscillator is 450 kilotwo branches which convert the frequency or cycles minus 350 lrilocycles or 100 kilocycles, and phase modulation on Wave energy into corre that producedby the 'second oscillator would be i0 sponding amplitude modulations on wave energy, 55,0 vkilocycles'lminus 450 kilocycles or 100'kilo` '10' with the modulation envelopes 180 degrees apart cycles. Thus We have twoiintermediate frequen-l` in phase, This phase difference ofthe modulacy outputs of the samey frequency and identical tions is produced by the converting systemsl I; F.1ampliers and selector vcircuits can be used. Which convert the frequency or phase rnodula lNow,`if the frequencyshifts (in accordance with A l5 tion on the Wave energy to amplitude modulasignals)` to 451. kiloovoles, the firstl oscillator l l tion for detection. In the novel receivers of the beating With this shifted signalA Wave Will Dro,- present application the reversal of phase'jof the'y 4duce afbeat frequencyv equal to 451 kilocycles modulation is accomplished in frequency 'con- `minus-350 kilocyoles--or ll'lkiloeycles, and the verting or changing detectors which reverse the second oscillator beating with the shifted signal 20 direction of the phase or frequency of the Wave f Wave willrproduce a` beat frequency equal to- 550 '20 energy. This makes it possible for-each`branch kiloeycles mlnus451 klooycles 0r 99 kiloeycles. of the back-to-back receiver systems for con- Notethat the direction Of frequency shift of one verting the phase or frequency modulation to of the resulting intermediate vfrequencies is in amplitude modulation to be substantially iden-v one direction andthe other in the other direc- .25 tical, yet the detected outputs will be l180 -lde-v-v ntion, in other Words,` the modulation 0f one I. F. 25 l v grees out of phase the Same as in the prior reils :reversed With respect-t0 they' modulatiQnOf ceivers. As is known in the art, the 180 degree j ithe other I. F. 'Aphase'shift (Which may be conphase relation of the yenvelopesl is desirable for sdered asa small frequencyy shift) iS reversed different reasons, an important reason being that in the-saine manner.' l i 1,30 unwanted amplitudeA modulations on the phasel l -This-broadprinciple as Outlined above' iS alJ- or frequency modulatedwave are cancelled in plieeble'tO-varibus types y0f phase or frequency the detector Outputs, f modulated .wave demodulators. The application An advantage gained by the use of this method `thereof to lthree ltypes of receivers Will now be of reversing the polarity of the modulation isr *..described- A'by-reference to the attached drawings ,35 that the two branches of the receiver Ymay utilize f wherein the three heures Showthree frequency 35 identical converting systemsv for converting `the 'or rphase modulated receivers wherein identical phase or frequency modulation to amplitude systems'for converting the original modulations modulation for detection. This-helps to obtain toemplitude modulations with opposed modulaa more accurate back-to-back balance since it tionenvelopes-are shown. is easier 4to produce two identical systems for Figure- 1 ShoWs a frequenorr modulated Wave 40 converting the -frequency or phase modulation receiver includinmeans Vfor beating the freinto amplitude modulation thanV it is to provide quelle-Y modulated Wave With oscillations 0n op-v two systems which convert in a uke manner but Hhesite Sides. ef the meen'frequency of the modu- With reversed characteristics to get the 180v de- .lated WaVe-, demodulatingnleanss of the sloping 45 gree phase relations between the amplitude filter? tvpevfand automatic frequency control "5 modulation envelopes desirable in the differential means associated With an oscillator` in the' reoutput of the detector system. ceiver. v'Figure 2v shows a! receiving system, re-

, The principle upon which thislsystem is based ySponsive t0 phase modulated Wave energy. Figis .that by heterodyningthe incoming signal with ure..3. is .a modification of vthe arrangement 0f 50 oscillators tuned to opposite sidesV of zero-beat Figure-2.A x50 with the signal, instantaneous beat frequencies Figure v'1 Shows hoW this reversal of lfrequency will beproduced wherein the deviations inphase :ory phase shiftmay be takenr advantage of to or frequency at signal frequency will bein op- -Produce a back-to-back frequency modulation .posed sense or phase or angular relation. lior receiver which uses converting filters having the 55 instance. in;v the case of frequency modulation same slope insteadl ofopposite slopes. as'used .in 5s the conventional back-to-back frequency modulation receiver such asA disclosed in my United States Patent #2,071,113, issued February 16, 1937. The signal is received on antenna I, amplified in radio frequency amplifier 2, and converted to intermediate frequency by detector 3 wherein the amplified signal is mixed with oscillations from high frequency oscillator 4. Intermediate frequency band-pass amplifier 6 selects the desired intermediate band of frequencies and feeds the same to two detectors 8 and 8. These two detectors cooperate with oscillators 1 and 'I' to convert the phase or frequency modulated rst intermediate frequency wave into two` new waves of a second intermediate frequency with the polarity or direction or sense of their frequency or phase modulations reversed. Oscillator 'I is tuned to one side of zero beat with the signal carrying rst intermediate frequency while oscillator 'l' is tuned to the other side of zero beat with the first intermediate frequency. For instance, if the frequency from. 6 is 450 klocycles, 'I may be tuned to 350 kilocycles and I to 550 kilocycles. The two sloping filters 9 and 9 connected to 8 and 8 respectively, have the same direction of slope as indicated by the curves, so that when fed frequency modulations of opposite phase the resulting amplitude modulations will have envelopes of opposite polarity. That is to say, the filters 9 and 9 are made identical and adjusted so that the I. F. carrier frequency at zero modulation is at the linear portion of the sloping part of their characteristics. When modulation is applied oneI. F. increases, the other decreases, and such changes are changed in each lter to a corresponding amplitude variation. The amplitude modulations are detected in diodes I0 and I0 which are connected in series with the polarity of one of them reversed so as to combine the resulting detected outputs in phase. This reversal for differential output is obtained by grounding the cathode of one detector, say I0', and taking the added modulation voltages from a point on the resistance adjacent the cathode of the other diode I0. The detected and combined outputs are fed to audio frequency amplifier II and made available for utilization at jack I3. Control potentials for automatic frequency control are also taken from the diode resistors and fed through time constant circuit I2 to reactance tube modulator 5. Reactance tube modulators of the type involved here are well known in the art and have been disclosed in several of my pending applications and in my patents.

Figure 2 shows how this method for reversing the direction of phase shift may be utilized in a phase modulation receiver. Unit 200 consists of the band-pass intermediate frequency amplifier of a superheterodyne receiver, such as, for eX- ample, unit 6 of Figure 1. The selected intermediate frequency energy is fed from amplifier 200 to detectors 20| and 20 I which cooperate with oscillators 202 and 202 tuned to opposite sides of zero beat with the I. F. phase modulated wave from 200 so as to reverse the direction of phase shift of the heterodyned outputs of one of the detectors 20| and 20V. These two heterodyned outputs are fed to the phase detector consisting of push-pull transformer 203, common leg transformer 20d, and diodes 205 and 206 with their resistors 2II and 2I8. This phase detector is of a known type which detects the difference in phase between the two waves fed to the two input transformers. Somewhat similar demodulatubes 304 and 3M.

'having tors have been described in my prior applications and patents. See, for example, my United States Patent #2,065,565, dated December 29, 1936. In these detectors a phase quadrature relation at zero modulations, between the voltages induced by 203 and 294 on the detectors 205 and 206, is

ymaintained. Then if the phase shifts (due to modulation) this phase relation is changed and the change in the resultant voltage on the detectors produces variations in their output commensurate with the extent of such variation. In this new system, however, if the wave from detector 20| shifts in phase 3l] degrees in the positive direction, the wave from detector 2M will shift 30 degrees in the negative direction. The total phase difference will then be twice that existing on one wave alone so that this receiver has a sensitivity which is twice that of the ordinary type of receiver which detects the phase difference between the phase modulated wave and an unmodulated wave.

The detected output appearing across diode resistors 2li and 2I9 is fed to audio amplifier 2I9 which makes the output available for utilization at jacky 220. This same detected output is also used for automatic frequency control on the beating oscillators 202 and 202'. The control voltage is fed through time constant circuit ZIE, 2I5 and grid resistor 2M to vary the control grid voltage of modulator reactance tube 297. Reactance tube 207 obtains its reactive plate circuit by virtue of the phase quadrature feedback through blocking condenser 208 and the phase shifting circuit consisting of resistor 209 and condenser 2I0. Oscillator 202 has reactance tube 201 connected to it and operates in thesame manner as the other oscillator and reactance tube. If desired, the automatic frequency control to one of the beating oscillators may be omitted since to do so merely reduces the sensitivity of the control, but sufficient control will still be available. Corresponding numerals primed have been applied to the control circuit for reactance tube 201. Reactance tube modulators for controlling the frequency of an oscillator are well known now in the art, and have been described in several of `my prior applications, and it seems unnecessary to describe the same here. See, for example, my application Serial #165,956, filed September 22,

1937, now Patent #2,156,374, issued May 2, 1929,

my application Serial,#l67,34=l, filed October 5, 1927, now Patent #2,156,375, issued May 2, 1939, my application Serial #233,719, filed October 7, 1938 and my application Serial #209,919, filed May 25, 1938.

Figure 3 shows how the off-neutralized crystal lter type of phase modulation receiver is connected to utilize this principle of reversing the polarity o-f phase modulation. The Vconverting circuit of Figure 3 filters and diode detectors 9, 9', II), and I0 of Figure 1. Detector 3 then feeds leads 300 and 30| and detector 3 feeds leads 390 and 30|". Transformers 302 and 302 feed identicalcrystal filters 303 and 393 which feed the diode-driver Band-pass transformers 305 and 305 feed diodes 306 and 306 from which the detected output and the automatic frequency control potentials are obtained.

The crystal filters comprising piezo-electric crystals 303 and3 may be both overor underneutralized. In any event, they are substantially identical and it is easier to produce two filters substantially identical characteristics than two filters having opposed characteristics.

may replace the converting mediate frequency at zero modulation ergy, f :and'fbeating 'said original phase or` fretion with thecarrier. In this manner4 the phase modulations (now reversed) are converted into amplitude modulations with opposed envelopes for detection in tubes 306. and 306. v

For a more detailed description of the converting filters see my United States Patent #2,085,008,

rdated June 29, 1937now Patent #2,085,008,

issued June 29, 1937, my Iapplication Serial #192,196, filed February 24, 1,938, my application Serial #165,056, filedv 4September 22, v 1937, now Patent #2,156,374,issued May2, 1939my application Serial #167,344, filed Octoberr 5, 1937, now Patent #2,156,375,- issued May2, 1939my application Serial #195,041, filed March 10,1938, my application Serial #178,655, filed December 8, 1937, now Patent #2,156,376, issuedvMay 2, 1939, my application Serial #242,469, filed `November 26, 1938 and my application Serial #186,273,1iled January 22, 1938. j v In Figure -2 the circuitspreceding the unit 200 have been omitted in the sake of briefness. UnitA 200 may be connected to the output of a first detector, such as 3 of Figure 1. In this kcase the leads to 4 and I2 are disconnected at the points Vmarked X in Figure 1.

What is claimed is;

1. The method of producing by means of phase or frequency modulated Wave energy` otherwave energies modulated in opposed sense or `polarity by phase or frequency modulations` corresponding to the phase or frequency modulations on the said first Wave energy which includes the steps o f,

generating oscillations of a ,frequency higher.

than the mean frequency of said Wave energy, beating said original phase or frequency modulated Wave energy with said generatedv oscillations of higher frequency to produce a first phase or frequency modulated beat note, orgeneratl:lng oscillations of a frequency lower than, the

mean frequency of said Wave energy, beating s aid original phase or frequency modulated Waveenergy with said generated oscillations of lower frequency to producey a second phase or frequency modulated beat notein'vwh'ich the sense or polarity of phaseor frequency modulation is opposite to thev senseor polarity of the phase or frequencymodulation's' on said rst beat note.

2l The method of producing by means of phase or frequency modulated Wave energy other phase or frequency modulated Wave energies in which the modulations correspond to each other and to the modulationsr on the original wave energy but are of unlike polarity o-r sense which includes the steps of, producing oscillations of a frequency higher than the mean frequency of said wave .quency of said firstbeat note.'

quency modulated Wave energy with said V,pro-

ducedioscillationsof a frequency lower than the :mean vfrequency of said phase or frequencyY modulated Wave energy to produce a secondI beat rnote, modulated in phase or frequency, of a mean frequencysubstantially equal to the mean fre- 3. -The method ofproducing by means of .phase ,or-frequency modulated Wave ,energy other Wave energies modulated in yopposed sense by phase or frequency. modulations corresponding to the phase or frequency modulations on the said rst .Waveenergy which includes the steps of, producingi'oscillations of a frequency exceeding the mean frequency of said modulated wave by a selected amount, producing other oscillations of -a frequency equal to the mean frequency of said modulatedlwave minus said selected amount, beating said original phase 'or frequency modulated Wave venergy with said first oscillations to -produce a first phase or frequency modulated -beat note of a mean frequency equal to said selectedairiount, and beating said original phase or v.frequency modulated Wave energy with said otheroscillations to produce a second phase or frequency modulated beat note, of '.a mean. frequency equal' to said selected amount, in which the sense or lpolarity of phase or frequency ymodulation is. opposite to the sense or polarity nal potentials'but are of unlike polarity or sense which includes the steps of, passing said energies through-pathsY of `substantially like characterisv tics Which convert said phase or frequency modulations into corresponding amplitude modulations of opposed polarity and demodulating the energies passed by said paths to reproduce the signal'. j 5'. Thel method of demodulating phase orfre- Wave energies through ,pathshaving substantially identical characteristics which convert the Y phase or frequency modulations on said Wave energy to corresponding 'amplitude modulations with envelopes degrees out of phase, demodulating the energies .-passed by said paths, and

`differentially combining the modulation compo-v nents to produce thesignal.

l 6. The method of demodulating Wave energy modulated in phase or frequency which includes stepsof, providing oscillations ofa frequency 'greater than the frequency of said Wave energy,

"quency modulated rWave energies in which vthe modulations correspond but are of unlike polarity or sense Which includes the steps of, passing said beating said original phase or frequency modulated Wave energy with said oscillations of greater frequency to produce a first phase orvfrequency modulated beat note, providing oscillations of a frequency less than the frequency of said Wave energy, beating said original phase or frequency modulated Wave energy With said oscillations of less frequency to produce a second phase or frequency modulated beat note in which the sense or polarity of phase or frequency modulationis opposite to the sense or polarity of the phase or frequency modulations on said first beat note, passing said beat notes through paths having substantially identical characteristics for converting said modulations to corresponding amplitude modulations, and combining the en.- ergies passed by said paths.

7. The method of demodulating phase or frequency modul-ated wave energy which includes the steps of, beating said original phase or frequen-cy modulated wave energy with oscillations of a frequency greater than the mean frequency of said original wave energy to produce a first beat note modulated in phase or frequency, beating said original phase or frequency modulated wane energy with other oscillations of a frequency less than the mean frequency of said phase or frequency modulated Wave energy to. produce'a second beat note, modulated in phase or frequency, of a mean frequency substantially equal to the mean frequency of said first beat note, passing said beat` notes through identical modulation converting baths, demodulating the energies passed by said baths, and differentially adding the demodulation components to reproduce the signal.

8. In a system for converting phase or frequency modulations on wave energy into wave energies correspondingly modulated in phase or frequency but of opposite sense, means for producing oscillations of a frequency lower than the frequency of said wave energy, means for beating said phase or frequency modulated wave energy with said lower frequency oscillations to produce a first phase or frequency modulated beat note, means for producing oscillations of a frequency higher than the frequency of said wave energy, and means for beating said phase or frequency modulated Wave energy` with said higher fre quency oscillations t0 produce a second phase or frequency modulated beat note the modulations on which are of a sense opposite to the phase or frequency modulations on the nrs-t Kbeat note.

9. In a system for demodulating phase or frequency modulated wave energy, means for providing oscillations of a frequency lower than the frequency of said wave energy, means for beating said phase or frequency modulated wave energy with said lower frequency oscillations to produce a rst phase or frequency modulated beat note, means for providing oscillations of a frequency higher than the frequency of said wave energy, means for beating said phase or frequency modulated wave energy with said higher frequency oscillations to produce a second phase or frequency modulated -beat note the modulations on which are of a sense opposite to the phase or frequency modulations on the first beat note, means for converting the modulations on said beat notes into corresponding amplitude modulations and means for detecting the amplitude modulations.

10. In a system for demodulating phase or frequency modulated Wave energy, two sources of oscillations one of which supplies oscillations of a frequency greater than the mean frequency of vsaid Wave energy the other of `which supplies oscillations of a frequency less than the frequency of said Wave energy, a first heterodyning detector excited by said wave energy and by oscil latory energy from that one of said sources which supplies oscillations of a frequency vgreater than the mean frequency of said wave energy, a second heterodyning detector excited by said wave energy and )by other oscillatory energy from the other of said sources which supplies oscillations of a frequency less than :the mean frequency of said frequency or phase modulated Wave energy, a pair of differential detectors, and frequency discriminating circuits coupling each of said heterodyne detectors to said differential detectors.

11. In a system for demodulating -phase or frequency modulated Wave energy, a rst source of oscillations of a frequency equal to the mean frequency of said wave energy plus a constant, a second source of wave energy of a frequency equal to the mean frequency of said Wave energy, minus said constant, a first heterodyning detector eX- cited by said w-ave energy and by oscillatory energy from said first source of a frequency equal to the mean frequency of said Wave energy plus a constant, a second heterodyning detector excited -by said Wave energy and by oscillatory energy from said second source of a frequency equall to the mean frequency of said wave energy minus said constant, a pair` of differential detectors, and substantially equivalent frequency discriminating circuits coupling each of said heterodyne detectors to said differential detectors.

12. The method of demodulating Wave length modulated wave energy which includes the steps of, beating said original wave length modulated wave energy with the oscillations of a frequency greater than the mean frequency of said original wave energy to produce a first beat note modulated in wave length, beating said original wave length modulated wave energy with other oscillations of a frequency less than the mean frequency of said wave length modulated wave energy to produce a second 'beat note, modulated in wave length, of a mean frequency substantially equal to the mean frequency of said first beat note, passing said beat notes through substantially identical modulation converting paths, demodulating the energies passed by said paths, differentially adding the demodulation components to produce a resultant characteristic of the signal and controlling the frequency of both of said oscillations, used in said beating processes to produce said first and second beat notes, in accordance with said resultant.

MURRAY G. CROSBY. 

